I'm a year late on this post, but I used pvc hoops on some of my raised beds. I like the rebar idea. I used that method on my first hardening hoophouse
http://imageshack.us/a/img215/1905/rebarassem.jpg . I drilled 7/8" diameter holes in the top of the sides of my beds, inserted the pvc tubing, then drilled in from the side and used a nail to secure it from pulling out
http://imageshack.us/a/img805/3019/hoopedbed.jpg . I used 10' long 1/2" PVC pipe for my 30" wide beds, and it was good height for peppers and taller veggies
http://img29.imageshack.us/img29/9866/hoopsp.jpg .
A word of Warning.... If you use Greenhouse Film with UV coating, you must paint the PVC with a latex paint. The PVC will react with the UV chemicals and the Film will become brittle and disintegrate within the first season. I use mine during April and October to prevent frost damage and gain a few weeks of growing season.
As far as filling beds, I make up a homebrew similar to Mel's mix and mix it 50% with pure compost. Each year I add 4" of height to my beds and then mix in 4" compost
http://imageshack.us/a/img801/6600/162af.jpg .